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Post by cyclecamper on Nov 22, 2016 23:03:23 GMT
I have a lot of complicated questions, so I'm going to attempt to organize this by addressing issues separately. But they are all about my listening / bass guitar practice / (converted family room) which merges into a rattly kitchen: about 17' 4" X 16' 6" with a half-vaulted ceiling. The ceiling is only about 8 feet high at the 17' 4" front end lower "dead end" wall with the speakers. The ceiling slopes up from that end at about 30 degrees and is about twice as high, 16' high, at the "live end" back 16' 4" wall, which is very irregular shaped down lower with a kitchen island countertop, refreigerator, etc. and entrances to other relatively absorptive (or will be absorptive) hallways and rooms. So the back kitchen wall at the tall end of the room is another r17' 4" wall that drops vertically from the acute 60 degree angle at the peak of the ceiling until it reaches an opening to the dropped ceiling over the open counter and kitchen at the back of this converted "family room". Multiple subs, including near the back wall.
The midbass and mid/high narrow planar dynamics are 7' tall line sources with a cylindrical wavefront rather than the usual spherical wavefront from a point source, and don't radiate upwards or downwards as much as most (they cancel up & down), but they spread sideways quite a bit, and the radiated acoustic power tends to drop linearly with distance instead of as a square from a point source...so they sound quieter when nearer and one one portion radiates directly to your ear, and above & below tend to cancel...but when you are farther back the volume drops with distance less than most.
I'm hoping to get setup to learn and use REW...but it's not going to happen yet. So for now I'm using rule-of thumb and physical measurements without any real acoustical measurements for a while yet.
Of course there will be all the required absorption of early reflections and boundary effects around the speakers at the "dead" end, and floor and ceiling treatments. So, like I said, I have many questions I want to ask, which means deferring many obvious issues, so the sequence of issues I raise may seem odd. The first issue I would like more clarity about is the standing wave modes of the long parallel side walls. I intend to use much of that wonderful overhead area for absorption and diffusion. WAF or SAF or whatever the politically-correct term is now, is not an issue...I live alone. If I mount overhead vertical absorption panels hanging down from the ceiling....literally hanging down like thick rigid absorptive vertical curtains...to help address the standing waves between the two parallel 16'6" side walls...what would the ideal placement be within the space of the room...just addressing the standing waves between the long parallel walls? One side of the room has more entranceways and an overhead air register, so I'm contemplating asymmetrical bass absorbers hanging down from overhead, in addition to soffit corner and wall absorption. There will be others, but this question is about vertical hanging absorption panels with their dual-sided faces parallel to the long side walls.
I like the possibility of perhaps leaving nearly half the ceiling unobstructed by using asymmetrical absorber placements. It's usually not advised, but here we are talking mostly about bass, and well overhead. If I can decrease the decay rate the bass is probably not going to sound like localized reflections from anywhere in particular anyway.
I understand that for the most part the thick Roxul rockwool absorbers are effective at the places where a standing wave has maximum velocity, not maximum pressure. I'm thinking about hanging them where the velocity maximums will be located for the first few modes. So I considered hanging them: (A) - at the midpoint between the long parallel walls for the 32 Hz fundamental = which would have one centered 8.75' from one side wall (B) - at the 1/4 point (probably foregoing the 3/4 point) for 98 Hz = 4.375' from the side wall (C) - at the 1/6 point (there is already one at the 3/6 point for (A) above, so maybe this is optional, and I would probably forego one at the 5/6 point) for 163 Hz = 2.91' from the side wall
(D) - at the 1/8 point (probably forego the 3/8 point, 5/8 point, 7/8 point)for 228 Hz = 2.1875' from the side wall (E) - at the 1/10 point (there is already on at the 5/10 point for (A) above, so maybe this is optional, and I would forego the 3/10, 7/10, 9/10 points) for 293 Hz= 1.75' from the wall
Questions: Have I got this whole velocity/pressure idea straight in my head? Is this efficient use of my resources for addressing some of this particular bass standing wave? From your real-world experience, assuming this type of approach among others, how many panels and where would you recommend, in addition to thick absorbers at the wall(s)? Assuming typical drywall on wood studs, what should I expect the relative strength of each harmonic likely to be? My speakers will be pumping as low as 32 hz into the room occasionally... What would you recommend as the relative proportions (relative area) of each of the absorbers?
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Post by rock on Nov 23, 2016 1:47:07 GMT
Measurement is not absolutely necessary but if you are thinking it is something you want to do, Do it NOW, first. If you do, you can see how your room changes and you may be able to answer some of your own questions. It's not hard and if you're not familiar with some of the concepts, now is the time to learn.
I don't know what effect panels will have at the places you're suggesting. Maybe try all of them one at a time and measure each one? OTOH, try the standard advice Ethan provides in his sticky OR wait to see what Ethan says.
Cheers, Rock
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Post by cyclecamper on Nov 23, 2016 3:08:31 GMT
Yeah I'm still reading and learning...he's pretty clear and consistent. Lots of misinformation out there on the internet.
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Post by cyclecamper on Nov 23, 2016 5:11:21 GMT
Another question: Besides hanging clouds and ceiling absorption panels, I am considering something that is usually not advised. I want to take 2' X 4' acoustical ceiling tiles, the cheap type usually in a suspended grid drop ceiling, and glue them to the ceiling upside-down. I can get them cheap because they are mass-produced and priced competitively. Then I want to glue a second layer, this time of 12" X 12" Armstrong 741 fine-fissured tongue and groove acoustical ceiling tiles for surface mounting onto the first layer. www.armstrongceilings.com/commercial/en-ca/commercial-ceilings-walls/fine-fissured-ceiling-tiles/item/741.htmlIn the past, I've used two pieces of 2' X 4' acoustical ceiling tiles, glued them to two more laid out cross-wise, to create a strong double-thickness 4' X 4' square, and then used latex glue to adhere acoustical foam to the surface...and mounted the whole thing 2 inches off the wall. I was pleasantly surprised and pleased with their performance into the mid-bass region. But I have no idea what to expect from putting two layers directly onto the ceiling, with only a few pieces of foam instead at the primary first reflection points on the ceiling. I'm reluctant to space the ceiling tiles off the ceiling, as they can eventually sag when exposed to humidity unless adhered to some more solid substrate or held up by their edges. It does cover a LOT of surface, but I'm concerned it might absorb only higher frequencies. I considered two layers of the cheaper tiles then having them sprayed with an acoustical cellulose product, but it's expensive to have a small space treated, and the resulting performance depends a lot on the diligence of the people applying the product. What do you think of the idea of treating the ceiling, and perhaps even everything overhead including side walls, with one or two layers of acoustical ceiling tiles, like they used to do in the old studios of the 1950's before Sonex and Auralex...back when tongue and groove acoustical tiles contained asbestos and were put on walls... Then I would hang absorbers, and even some diffusers, on top of the ceiling tiles...
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Post by cyclecamper on Nov 23, 2016 5:40:31 GMT
I built 30 DIY frames from GIK. I've just started stuffing and covering them. Many of them will mount overhead and will have an additional chamber with a sealed back behind them of various depths.
I already put pegboard on the backs. If I stuff the additional back chambers, the pegboard will be mostly transparent to the bass, and the treble & mids already somewhat attenuated by the first 4" of Roxul. So I suspect that might be an OK rather balanced broadband absorber with a step in the absorption graph at some frequency around 500Hz (just a guess)? Or I could take a holesaw now and put some 2" holes thru the pegboard. I don't have any real measurement data to work with, for the room or the absorbers, so my gut inclination would be to play it safe and open up the pegboard some, but it seems enough bass below 250 should go right thru anyway. And for bass that doesn't get thru, I might get some damped motion of the pegboard and some diaphragmatic absorption in response to pressure rather than velocity.
But if I want to tune the rear chambers behind the 4" absorbers low as real miniature Helmholtz resonators with virtual walls between (due to equal pressure planes), I didn't do the math but I think the Masonite should be thicker and I should plug 3/4 of the holes in the pegboard by gluing strips of thinner Masonite over entire rows vertically and gluing small strip over half the holes horizontally. I think with the thin Masonite, the holes don't model as inductors anyway, more like resistors, and the chamber behind as a capacitor. But I could save some money on stuffing by making a narrower bandwidth abck-chamber absorber, at great risk of tuning it wrong without taking the measurements and doing the math.
I'm inclined to leave the Masonite pegboard in place on the back, neither blocking more holes nor enlarging them, and stuff the back chamber behind it. The Masonite will do something, but I'm not sure what...it may do just what I want, extend the absorption lower and limit the amount of midrange absorption to match. I will vary the depth of the back chamber behind the original 4" thick frames, and the ones at human height on the side walls may not get back chambers at all, in order to not constrict the usable space within the room.
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Post by cyclecamper on Nov 23, 2016 5:54:59 GMT
I've also been looking into various diffusers for various locations. Perhaps some fractal diffusers under the countertop? A skyline looks like a lot of work and weight and materials. I would love some nice RPGs but it is difficult to justify the expense for even a wood kit. But I am seriously considering making a few very large convex shapes because I think it can be dome cheaply. They don't really do the same thing or have the same effect in the far field as a good diffuser, but they should be somewhat better than flat parallel walls, and complicate the modes and break up simple axial mode standing waves into more complicated paths. I was considering mounting a long 2" X 6" to the wall vertically, and curving sheets of Masonite on either side of the board to the wall, making a 16 foot wide convex curved surface. But it raises a lot more questions about how to damp it, whether to stuff it, how much to brace it, whether to put holes in it, whether to cover it, etc. etc. Still, it's so cheap and better than nothing. I'm surprised more people don't give it a try, and leave some wall space flat and bare instead.
What do you think of such convex "spreaders" assuming they are large enough to have some effect at frequencies that matter?
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Post by Hexspa on Nov 23, 2016 8:56:33 GMT
Hi cyclecamper. Sounds like you've read a lot. I'm quickly inundated by so much text. Please forgive me and allow me to contribute. You've likely read Ethan's articles and stickies. Please consider reading a PDF I've donated for clarification on my opinions: hexspa.com/listening-room-ebookI think the consensus is to prioritize for broadband treatment and only add diffusion as a finalizing measure. I understand your idea to hang absorption between the parallel walls. Like Rock said, that may or may not be the best positioning - consult your REW results. There's something called the Feynman technique which says that proof of understanding is directly correlated to how simply you can explain it. In that light it seems you're still a bit unsure. In that regard, I'd say - find your listening position, measure, treat RFZ and corners then measure again. You'll be far better off by implementing one or two steps at a time than endlessly philosophizing and weighing your options. Respectfully, -m
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Post by cyclecamper on Nov 23, 2016 17:01:04 GMT
Yes... I need to focus on getting equipped to perform meaningful measurements. But I'm starting with some obvious things, like stuffing the fireplace to turn it into a bass trap LOL.
There are some things that I would like to do next, for practical construction sequence reasons. One is to apply full treatment to the ceiling before I hang additional absorbers or clouds etc. The other is to hang these absorber panels to dangle from the ceiling.
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Post by Hexspa on Nov 24, 2016 10:25:38 GMT
If you're referring to "acoustical tiles" I hypothesize your disappointment.
I suggest moving directly to broadband absorption.
The choice is yours!
Happy Thanksgiving,
-m
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Post by cyclecamper on Nov 26, 2016 14:40:30 GMT
Since the back of my room has some height, if I used some RPG QRD diffusers I'm having some difficulty deciding where to place them. - the "LIVE END" of this LEDE listening room - human-height - a least a few feet from any seating
I guess this narrows it down to either making a false back wall across that island countertop or on the back ends of the two terrible parallel side walls.
Which brings up the question of when to diffuse horizontally and when to diffuse vertically...I haven't found any info on that subject...yet. Still looking.
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Post by Hexspa on Nov 27, 2016 11:41:17 GMT
You should diffuse horizontally (vertical diffuser orientation) and provide 1' of distance from LP for every inch of diffuser depth.
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Post by Ethan Winer on Nov 29, 2016 19:47:14 GMT
... QRD diffusers I'm having some difficulty deciding where to place them. The usual place for diffusers is on the rear wall behind the listening position. Have you seen my All About Diffusion video? I think it answers all your questions, but I'll add this: 1D diffusers are almost always oriented upright to scatter sound left and right. It's not usually useful to scatter sound down into a carpet or up at the ceiling. By extension, 1D diffusers are usually placed on walls, but 2D "skyline" types are better on the ceiling because scattering in all four directions makes sense there. --Ethan
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Post by cyclecamper on Dec 1, 2016 15:49:48 GMT
Thanks for engaging. I did pick up 12 used 1D RPG QRD diffusors from a friend. And I also picked up a bunch of cheap fractal diffusors made in Latvia out of EPS expanded polystyrene beadboard, which I'm spraying with epoxy (never polyester resin which has styrene which will melt the foam). I have some relevant experience; surfboard sometimes use similar methods.
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Post by cyclecamper on Dec 1, 2016 16:59:40 GMT
I would love your perspective and opinion of my plan for the panels hanging vertically, especially since they will be so absorbent above the "live end" of the room.
With my half-vaulted ceiling I have the overhead space for hanging absorbers within that overhead space of the live back end of the room, so it's going to be absorptive overhead; thick hanging vertical "space divider curtain walls" within the space (not near the walls) and one or two horizontal clouds. So perhaps vertical 1D diffusion might result in more absorption? My gut inclination would be to hang 1D arrays at an some slight angle. I'm also considering staggering some of the QRD units different depths spaced out from the wall; would that arrangement extend their bandwidth into deeper bass? I'm also curious about their behavior with wavefronts that don't arrive at 90 degrees to the units...if sound arrives at a complex compound angle, are they effective into lower frequencies? I guess there are two issues for a vertical unit that diffuses horizontally; 1) how it handles sound arriving from one side or the other 2) how it handles sound arriving from above or below. I understand how they work for direct sound and simple modes for a back wall; but these are likely to be used in the rear side walls, the LE part of the LEDE. The back wall already has some complex shapes, and is getting some fractal diffusors for the higher frequencies. They would really benefit from some staggering of some panels to repeat the fractal pattern larger, for lower frequencies.
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Post by Ethan Winer on Dec 4, 2016 17:17:26 GMT
It's not clear to me what you mean by hanging diffusers. Do you mean hanging out in the air?
You ask good questions about sound arrival direction. I know that sound coming from the sides still gets scattered, but I'm not sure about sound from above and below. Of course, sound in most rooms doesn't emanate from the floor or ceiling! Google may have something to offer. If you find a believable explanation please post it here.
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